The present invention relates to method and apparatus for preparing the end of a coaxial cable for termination.
Coaxial cable of the type comprising a signal conductor, a surrounding layer of primary insulation, a braided shield, and an outer insulative jacket is well known. Such cable is typically terminated to a coaxial terminal of the type described in U.S. Pat. No. 3,323,098 and sold by AMP Incorporated as its COAXICON contact. Such contacts have a pin or socket portion which is terminated to the signal conductor and an outer tubular metal shell which is terminated to the braided shield. Before termination, the cable must be prepared by stripping the outer jacket to a second distance from the end of the cable to expose the shield, and stripping away the shield to a first distance less than the second. Additionally, the signal conductor must be exposed toward the end and the shield must be flared to facilitate termination.
U.S. Pat. No. 3,555,672 discloses apparatus and method for accomplishing a coaxial cable termination as described above. According to the method, two sets of blades engage the cable simultaneously at the first and second distances from the end, and are rotated about the cable to cut through the outer insulation and braid at said first distance and to cut the outer insulation at said second distance. The cable is then withdrawn while both sets of blades remain engaged, and the outer insulation between said second distance and said end and said braid between said first distance and said end are removed as a unit. The exposed primary insulation is subsequently cut circumferentially between the first distance and the end and the slug of primary insulation is pulled off to expose the signal conductor. The shield is then flared by gripping the end of the signal conductor and twirling it, the outer jacket being firmly clamped proximate the exposed shield. Alternatively, the end of the primary insulation is gripped and twirled prior to stripping, and the slug is subsequently cut and stripped. Either way, the rotary motion of the primary insulation imparts a flare to the shield.
The above described method works well enough where the primary insulation is polyethylene or other relatively hard material. Recently, however, foamed tetraflouroethylene (TFE), sold under the trademark Teflon by DePont Corporation, has seen increased use due to its good dielectric properties. W. L. Gore & Associates, Inc., makes a coaxial cable for foamed TFE primary insulation, which is in the form of a continuous strip helically wrapped about the signal conductor. TFE insulation is difficult to cut, though, which causes several problems if the cable is prepared by known methods. In order to completely sever the shield, it is necessary for the blades which cut it to penetrate the primary insulation. If the blades making the first cut remain engaged while the outer insulation and braid are removed from TFE primary insulation, the blades will pull the helical wrap out of the shield. An additional problem is the difficulty in cutting completely through TFE primary insulation without severly scoring the signal conductor; an incompletely severed slug likewise leads to pulling out the helical wrap.